Principles for selecting storage tanks

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1.1 Above-ground storage tanks 1.1.1 Vaulted storage tanks These types of storage tanks are widely used; they are typically employed for petrochemical products with a flash point above 60°C. They can be used to store materials at room temperature as well as those at higher temperatures (up to 200°C). 1.1.2 Floating roof tanks: The tank roof is positioned above the liquid surface of the stored medium and rises and falls with it. There is essentially no gas space between the floating roof and the liquid surface, which reduces gas evaporation losses and also lowers the degree of environmental pollution caused by gases. Due to the gap between the side of the tank top and the tank wall, a small amount of rain, snow, and wind-blown dust may seep into the tank; therefore, it is only suitable for storing lightweight liquid petroleum products (with a flash point of less than 60°C) for which the requirements regarding water and dust resistance are not extremely strict. This structure is more suitable for storage tanks with a volume greater than 1x10 m3. For light diesel, which requires large-volume storage tanks, floating roof tanks should be used when the capacity of dome-shaped tanks is insufficient. Due to the constraints of the sealing system design, the operating temperature of the medium generally does not exceed 70°C. 1.1.3 Internal floating roof tanks: Internal floating roof tanks are those that have an additional floating roof added to the arch-shaped roof tank. In addition to reducing evaporation losses of the stored material and minimizing pollution from gases to the surrounding environment, they offer better waterproofing and dustproofing properties compared to ordinary floating roof tanks; hence they are more suitable for storing petrochemical products for which high standards regarding product quality are required. When the flash point of the material is below 60°C and the volume of the storage tank is less than 1×10m3, a storage tank with an internal floating roof structure is recommended. 1.1.4 Spherical and horizontal cylindrical storage tanks: Storage tanks of this type can be used to store liquefied petroleum gas, light gasoline, liquid ammonia, and inert gases, depending on their design pressure. In addition, horizontal cylindrical storage tanks are also commonly used to store residual liquids recovered from oil and gas venting systems, chemical reagents, and as storage tanks in vacuum systems. 1.1.5 Gas Cylinders: Commonly used are wet-type gas cylinders, which are primarily employed for collecting and storing combustible gases as well as inert gases in oil and gas venting systems. 1.2 Underground storage tanks As mentioned earlier, due to factors such as high investment costs and long construction periods, this type of storage tank is rarely used; it is only chosen in situations where there are certain special requirements from the perspective of the processing process. For example, the fuel stations used for internal use in petrochemical enterprises and those in cities typically employ underground buried storage tanks (horizontal cylindrical structures), and the transfer storage tanks used for unloading crude oil from trains are also of the underground buried type. In summary, when storing petrochemical products and other fluids in different external environments, storage tanks with varying structures and installation methods should be selected based on the specific conditions of each case. The tank selection table lists the petrochemical products and other fluids suitable for storage in above-ground steel tanks of various designs.